Analog fiber optic links are commonly used to deliver analog signals by optical fiber to remote units. The analog signals can be periodic, such as sinewaves, which can be used to generate clock signals at the remote units. If the optical fibers are split from a common optical source, the clock signals can be synchronized to each other.
FIG. 1 shows a known method 100 for using a fiber optic link in a system to distribute an analog signal. At 110, the system generates or receives a periodic electrical signal. At 130, the system converts the electrical signal to an optical signal. At 140, the system amplifies the optical signal. At 150, the system splits the amplified optical signal into several optical signals and transmits the optical signals into respective optical fibers. The optical fibers extend from a local unit to various remote units. At 160, a remote unit receives the respective optical signal from the respective optical fiber. At 180, the remote unit converts the received optical signal back to an electrical signal. The electrical signal at 180 is intended to resemble the periodic electrical signal at 110, so that a zero-crossing of the signal at 110 occurs at the same time as a corresponding zero-crossing of the signal at 180. The electrical and optical signals in method 100 are all periodic, and all have the same frequency.
In practice, there are various random noise sources in the system that can affect the signal. The addition of this random noise to the signal can shift the zero-crossings of the signal at 180 so that some occur slightly too early and some occur slightly too late. If the zero-crossings of the signal at 180 are used to generate a clock signal for an analog-to-digital converter, the random noise can produce timing errors in the clock signal, which in turn adds jitter to the measurement. In general, it is desirable to reduce the noise sources wherever possible, in order to keep jitter to a minimum or a tolerably small value.